Wind turbines produce power proportional to the swept area of their blades, and the amount of air flow passing over the blades at any given time. Various design choices such as rotor diameter, blade length and load limitations are considered during design and fabrication of a wind turbine. Longer blades provide for more energy production in low winds. However, longer blades require more materials, higher manufacture and transportation costs, larger and more robust rotor design to support the added weight of the longer blades, and failsafe systems for preventing potential damage to the turbines in high wind situations as the longer blades may produce damaging levels of torque at high wind speeds.
Conversely, using shorter blades has its own set of drawbacks. For example, in low winds shorter blades may not have enough surface area to produce enough torque to move the rotor, thereby producing no power.
Regardless of size, all wind turbine blades are limited in overall efficiency due to various resulting properties of the air flow. Due to the rotational movement of the blades during operation, at least a portion of the air flow impacting the blade is converted to a radial component moving about the length of the blade from the root toward the tip of the blade. FIG. 1 illustrates a standard wind turbine 10 with a mast 12 supporting a hub 14 from which a plurality of blades 16 are supported. The mass of air affected by the turbine forms a stream tube as the wind must slow down due to energy extracted by the turbine. Wind W directed at the turbines will have an initial area as indicated by the circle 18. As the wind W reaches the blades 16, the air flow has two components, namely an axial flow WA and a radial flow WR, with the area of the wind flow expanding radially as indicated by circle 20 due to the conservation of mass flow rate along the stream tube. The flow continues to expand radially downstream, as indicated by the increased area at circle 22, since the pressure in the wake must return to the atmospheric pressure after a pressure drop experienced by passing though the rotor disc. Based on the conservation of momentum, this radial flow WR reduces the efficiency of the turbine since it creates a radial force from the available total force from the wind. This radial force is not contributing to any torque or power produced by the rotor.
The present disclosure addresses these and other similar problems resulting from conventional blade design. It allows the blade to convert part of that radial force into a tangential force by redirecting the radial flow WR, thereby increasing the torque and power extracted by the turbine.